Two-dimensional correlation spectroscopic studies on coordination between organic ligands and Ni2+ ions

Differentiation of ethanol-water clusters in Fenjiu by two-dimensional correlation fluorescence and Raman spectra

The taste of different flavor liquor is multifarious, but the same brand liquor with different quality is truth. The essence of supramolecular ethanol-water clusters and their intrinsic structural differences in three kinds of Fenjiu are studied by two-dimensional correlation spectra (2D-COS) of fluorescence and Raman. The 2D-COS of fluorescence reveals the prominent emission peaks of three Fenjiu are apparently different. The central fluorescence peak of Fenjiu (a) is located at 330 nm, corresponding to the cluster of (H₂O)_m(EtOH)_n. In Fenjiu (b), the emission peak appears near 310 nm, while those of Fenjiu (c) appear mainly near 310 and 373 nm, corresponding to the clusters of (H₂O)(EtOH)_n and (H₂O)_m(EtOH), respectively. Based on 2D-COS of Raman, the peak of Fenjiu (b) at 3440 cm^-1 changes initially, indicating its disorder degree is getting higher with continuous dilution with water. However, along with the dilution of Fenjiu (a) and Fenjiu (c), the peak located near 3200 cm^-1 changes in priority, indicating that the degree of association between ethanol and water is high, and the clusters formed there are stable. Therefore, this work provides the combined methods to distinguish different supramolecular sets in Fenjiu, applying liquor differentiation in the future.

Exploring two-trace two-dimensional (2T2D) correlation spectroscopy as an effective approach to improve accuracy of discriminant analysis by highlighting asynchronous features in two separate spectra of a sample

This study aims to demonstrate two-trace two-dimensional (2T2D) correlation spectroscopy as an effective tool for improving the accuracy of discriminant analysis. Because 2T2D correlation analysis allows sensitive capturing of asynchronous spectral behaviors between two compared spectra of a sample, the subsequent asynchronous correlation features are expected to reveal more sample-to-sample characteristics and discriminants than the original spectral feature. Initially, near-infrared (NIR) spectroscopic authentication of pure olive oil was performed using the spectra collected at 20 °C and 41 °C. When the 2T2D slice spectra of the samples were used for the discriminant analysis, the authentication accuracy reached to 100%, while became degraded in the cases of using the spectra collected either at 20 °C or 41 °C. Furthermore, a simple strategy of utilizing the average spectrum of one sample group as the reference spectrum in the 2T2D correlation analysis was proposed for two-group discrimination and evaluated for the NIR identification of the geographical origins of agricultural products (milk vetch root (MVR) and perilla seed samples). Because the average spectrum of one sample group was used for comparison, dissimilar constituent compositions of the samples in another group were better observed, thereby improving the accuracy of discrimination of the geographical origins of the samples in both cases. The overall results demonstrated that 2T2D correlation analysis is effective for highlighting the minute asynchronous spectral features of a sample and can be expanded for diverse vibrational spectroscopy-based discriminant analyses.

Synthesis, Photophysical Properties, and Metal-Ion Recognition Studies of Fluoroionophores Based on 1-(2-Pyridyl)-4-Styrylpyrazoles

A convenient access toward novel fluoroionophores based on 1-(2-pyridyl)-4-styrylpyrazoles (PSPs) substituted at position 3 with donor or acceptor aryl groups is reported. The synthesis proceeds in two steps: the first one via Wittig olefination of the appropriate 4-formylpyrazole and then Mizoroki-Heck coupling to yield the desired products in an overall yield of up to 69%. Photophysical properties of products (4-styryl) and their intermediates (4-vinyl) were explored, finding that they have strong blue-light emission with high quantum yields (up to 66%) due to ICT phenomena. The 3-phenyl PSP was studied as a turn-off fluorescent probe in metal ion sensing, finding a high selectivity to Hg2+ (LOD = 3.1 × 10-7 M) in a process that could be reversed with ethylenediamine. The sensing mechanism and binding mode of the ligand to Hg2+ were established by HRMS analysis and 1H NMR titration tests.

A Novel Approach Based on Two-Dimensional Correlation Spectroscopy to Determine the Stoichiometric Ratio of Two Substances Involved in Intermolecular Interactions

A novel technique called AOSD@Job's, combining asynchronous orthogonal sample design scheme (AOSD) with Job's method, is proposed to estimate the stoichiometric ratio of two substances that form a supramolecular aggregate under intermolecular interactions. First, a mathematical analysis was performed along with the procedure of the AOSD@Job's method. Then, the validity of the AOSD@Job's method was manifested by computer simulation on two model systems. Finally, the AOSD@Job's method was applied on two real chemical systems. The stoichiometric ratio between the coordination complex of Ni²⁺ and ethylenediaminetetraacetic acid disodium salt (EDTA) was estimated to be 1.0. Benzyl alcohol (BA) and β-cyclodextrin (β-CD) were determined to form a 1 : 1 host-guest complex. These values were consistent with the values reported in the literature. Compared with the traditional Job's method, the AOSD@Job's method has an evident advantage since it is still valid even if all the peaks of the supramolecular aggregate severely overlap with the peaks of the substances that form the aggregate.

Synthesis of Fluorescent 1,7-Dipyridyl-bis-pyrazolo[3,4-b:4',3'-e]pyridines: Design of Reversible Chemosensors for Nanomolar Detection of Cu2

An efficient access toward novel tridentate ligands based on 1,7-dipyridinyl-substituted bis-pyrazolo[3,4-b:4',3'-e]pyridines (BPs) and their usefulness as fluorescent probes for cation detection is reported. The synthesis proceeds by a three-step sequence starting from 2-chloropyridine (1), all reactions were performed using microwave radiation under solvent-free conditions, and an overall yield of up to 63% was obtained. Photophysical properties of three representative 1,7-dipyridinyl-BPs (PBPs, 6a-6c) substituted at position 4 with different donor (D) or acceptor (A) groups were investigated. Compounds exhibited large Stokes shift in different solvents and strong blue light emission in both solution and solid state, and quantum yields were as high as 88% for some of them; thus, a twisted intramolecular charge transfer (TICT) fluorescence mechanism characteristic of the 1,4,7-triaryl-BPs was confirmed. The 4-phenyl-substituted probe (Ph-PBP, 6b) was used successfully in the detection of some metals (Cu2+, Co2+, Ni2+, and Hg2+) by fluorescence quenching phenomena, which could be reversed in the presence of ethylenediamine. This probe showed a greater sensitivity toward Cu2+ in concentrations as low as 26 nM, and in the process of "on-off-on" for this fluorescent molecular switch, only 1 equiv of the analyte was used.